1. Field of the Invention
The present invention is directed toward an apparatus for automatically monitoring and controlling the light emitted by an illuminator for a multi-objective optical instrument, such as a microscope.
2. Description of the Prior Art
Early optical instruments, such as microscopes, were basically very simple devices and, as such, only required existing light to illuminate the objects being viewed. However, as microscopes became more sophisticated and capable of higher and higher powers of magnification, it was necessary to provide a separate light source to sufficiently illuminate the specimen. A simple incandescent light with an on/off switch provided a solution for a period of time. However, the incandescent light was designed to give off a constant level of light. Therefore, it would not emit sufficient light in some instances, while producing too much light in others. As a result, some operators suffered from eye fatigue.
In order to overcome this situation, a rheostat was added which enabled each operator to individually control the level of light.
This system worked fairly successfully, but did suffer from a drawback when multi-objective rotatable nosepiece assemblies were introduced. Each objective mounted to the nosepiece shell required, generally, that the light be adjusted to accommodate for aperture size. Consequently, the operator was continually adjusting the level of light each time the power of objective was changed. Further, as slides were changed from one to another, the light requirement would also change. For instance, going from a transparent slide to a translucent slide would require more light from the illuminator. Accordingly, in addition to compensating for the objective power in place, the operator was also continually adjusting the rheostat to adjust for the transparency of the slide being viewed.
U.S. Pat. No. 4,241,251, issued Dec. 23, 1980, to K. Yonekubo, shows a microscope which utilizes an automatic switching system for controlling the light. A series of screws of various lengths are situated such that when detected by a microswitch, the illuminating light is adjusted relative to the power of the objective in place. This system has several inherent problems. It is necessary to insure that each screw is set to the exact and proper height. Further, a plurality of microswitches are necessary which must be located and accurately mounted to the instrument. These switches serve only to additionally complicate the instrument. Still further, and most importantly, this system only detects the objective which is in place. It does not detect that light which is reaching the observer. Consequently, the light requirements may not be fully met relative to the type of slide specimen being viewed.
In a second embodiment of the Yonekubo patent, a light emitting diode is arranged in a microscope so that light emitted from the diode reflects off a chamfered surface of an objective. Each objective would have a different chamfer. Light receiving elements are arranged in varying positions and detect light reflected off the chamfered surface of the objective. The illumination may be controlled based on the information received. This embodiment necessitates that the chamfered surfaces on the objective be held to fairly close tolerances. Also, a plurality of light receiving elements must be used to receive the information from the light emitting diode. Consequently, the cost and complexity of the instrument increase. This embodiment, similar to the one described above, does not detect the amount of light being transmitted to the observer. It merely detects which objective is in place. It cannot compensate for specimen variations which require changes in lighting.
Another illuminating system is shown and described in U.S. Pat. No. 3,833,282, issued Sept. 3, 1979, to G. Kappel et al. The illumination system set forth therein has a lens system whose focal length may be varied to suit the field of view of an objective. The variation in the lens is accomplished by response to a reference signal sent by, for instance, one of a plurality of photocells.
The apparatus described by Kappl et al is quite complicated, requiring a reversible drive motor and a clutch connected to a lead screw which in turn carries the variable lens system. Reference marks on the nosepiece are detected by the photocells which in turn pass on the information to an evaluator which supplies the information to a data converter which in turn generates a set point relative to the information received.
This system is quite costly resulting from the sophistication of parts used and from the complexity of construction details. The system further suffers from the drawback that the grooves formed in the nosepiece may become soiled or tarnished which would alter the signal received by the photocell and sent on to the converter. Further, the system does not detect the light available to the observer and adjust it to optimum. It merely detects the objective in place and adjusts the light relative to that objective. Therefore, the light produced by this system may not be what the observer actually needs to properly examine the specimen.
The invention, as set forth and described in detail hereinafter, overcomes the problems encountered by the devices described above, as well as others.